Process for the production of uranium hexafluoride

ABSTRACT

The production of UF 6  in which UF 4  is reacted with air or oxygen in the presence of a catalyst at 500° to 700°C. The solid byproduct of this reaction is reduced with hydrogen in the presence of a catalyst at 400° to 600°C. Fresh UO 3  may also be reduced with hydrogen in the same reactor as UO 2  F 2 . The reduction product or products are reacted with hydrogen fluoride at 400° to 600°C, producing UF 4  which would be recycled for further reaction to produce UF 6 .

The invention described herein relates to the conversion of uraniumtetrafluoride (UF₄) to uranium hexafluoride (UF₆) by a process whichdoes not require the use of elemental fluorine.

The conversion of UF₄ to UF₆ is currently achieved by the reaction ofUF₄ with elemental fluorine. However, the use of fluorine on a largescale is expensive and presents serious corrosion and toxicity hazards.For those nations, particularly, which do not possess an establishedfluorine generating capacity and which also possess significant uraniumore reserves, it is highly desirable to discover a practical method forthe preparation of UF₆ which does not require the use of elementalfluorine at any stage.

The only method known to date for achieving this aim has been disclosedin the U.S. Pat. Nos. 2,535,572; 2,910,344; 3,009,768, in the BritishPat. No. 897,793, and in the German Pat. No. 1,148,533. In each case,the process is based on the reaction:

    2UF.sub.4 + O.sub.2 → UO.sub.2 F.sub.2 + UF.sub.6   ( 1)

the UO₂ F₂ so formed can be recycled to UF₄ by the reactions:

    UO.sub.2 F.sub.2 + H.sub.2 → UO.sub.2 + 2HF         (2)

and

    UO.sub.2 + 4HF → UF.sub.4 + 2H.sub.2 O              (3)

the oxidation reaction (1) was studied in 1945 by Fried and Davidson,USAEC Document AECD 2981 (1945), and in 1950 by Kirslis, McMillan andBernhardt, USAEC Document K567 (1950), who "found that no uraniumhexafluoride was detected on passing oxygen over UF₄ until the reactortemperature reached 740°C." In early development work, Ferris, USAECDocument ORNL-2180 (1957), reported that "the rate of oxidation is notvery rapid at temperatures lower then 750°C, a fact which could restrictindustrial application of the reaction."

The feasibility of producing UF₆ from UF₄ by oxidation with dry air oroxygen in a fluidized bed reactor at temperatures from 700°-850°C wasshown by Scott, Adams and Bresee, USAEC Document ORNL-2797 (1960).However, they observed many temperature-dependent side-reactions atthese temperatures which decrease the product yield, and corrosionreactions which limit the practical application of the primary reactionin industry. When impure UF₄ was used as the feed material for 29 hr ata temperature of about 710°C an 18 per cent yield of UF₆ was obtainedand the corrosion of the Inconel reactor was said to be prohibitive.

Pilot plant studies carried out in South Africa on the oxidation of UF₄also showed tht the very high operating temperatures led to extremecorrosion of the fluidized bed reactor, extensive sintering of the UF₄,and the formation of a liquid phase consisting of a mixture of variousintermediate uranium fluorides such as UF₅, U₂ F₉ and U₄ F₁₇. Thesepilot plant studies are disclosed in Document PEL-121, Vol. II (1965) ofthe Atomic Energy Board of South Africa and in the Twelfth Annual Report1968, p. 11 of the Atomic Energy Board of South Africa. A small Inconelreaction was corroded through after 700 hours of intermittent operationat temperatures up to 810°C. A moving bed reactor was also considered tobe of doubtful feasibility mainly because of the problems of handlingthe liquid phase arising from intermediate fluorides formed in thetemperature range 700°-800°C. For these reasons, the process was notconsidered to be feasible, and further development was abandoned.

The present invention discloses a process for the production of UF₆ fromUF₄ by the reaction of the UF₄ with air or oxygen in the presence of acatalyst, the use of which leads to economical rates of UF₆ productionat temperatures of 500°-700°C and reduces the detrimental effects of UF₄sintering, and the extent of corrosion.

The same catalyst may be recycled in the UO₂ F₂ product of the oxidationreaction with advantage in that it increases the rate of reaction of theUO₂ F₂ with hydrogen, and allows a temperature in the range of 400-600°Cto be used compared with the 600°-700°C used in the present art. Thecatalyst may then be further recycled in the UO₂ product which can beconverted to UF₄ by reaction (3).

A further advantage may be gained by feeding UO₃ into the process in thereduction stage as it has now been discovered that the reduction of UO₃to UO₂ is also catalyzed by the same catalyst.

It has now been discovered that a series of platinum group metalssupported on a suitable solid support are effective catalyst forreactions (1) and (2) at a temperature of 500°C or above. It has alsobeen discovered that gold and silver supported on a suitable material,and unsupported cobalt oxide and hydrated platinum oxide, PtO₂. xH₂ O(Adams Catalyst), and unsupported finely divided platinum are alsoeffective as catalysts for the oxidation reaction.

In the following, "catalyst" is taken to mean a material added to thereactants in the form of an active metal supported on a suitablesubstance, or an unsupported active metal or metal oxide.

The following examples of the invention are described in order toillustrate the effect of some of the various parameters of selectedmetals, selected supports, concentration of catalyst, and particle-sizeof support, on the catalysis of reactions (1) and (2).

Rates of conversion of UF₄ to UO₂ F₂ and UF₆ were determined by studyingthe rate of loss of weight of a sample of UF₄ when heated in anatmosphere of dry oxygen gas, the sample of UF₄ with and withoutcatalyst being placed in the sample holder of a conventionalthermobalance. A typical platinum catalyst is prepared by mixing anaqueous solution of chloroplatinic acid with the finely-divided supportmaterial, evaporating the mixture to dryness and heating the solid soobtained in hydrogen gas at 400°C to obtain platinum metal deposited onthe support. A commercially-available platinum on alumina catalyst isalso equally effective. The concentration of platinum metal on aluminais usually in the range 0.1 to 5.0 per cent by weight relative toalumina, and the concentration of catalyst used was in the range 0.2 to10.0 per cent by weight relative to UF₄.

The times required for 90 per cent reaction of UF₄ with oxygen attemperatures of 500° to 640°C and catalyst concentrations from 0.2 to1.0 per cent for platinum on alumina are given in Table 1.

                  TABLE 1                                                         ______________________________________                                        RATES OF REACTION OF UF.sub.4 WITH OXYGEN AT VARIOUS                          TEMPERATURES AND CATALYST CONCENTRATIONS*                                     Tempera-                                                                             Time Required for 90% Reaction (minutes)                               ture   Catalyst Concentration                                                 °C                                                                             0%          0.2%    0.5%  1.0%                                        ______________________________________                                        640    Slow, 35% re-                                                                              26.0    22.0  13.0                                               action in 40                                                                  minutes                                                                620     slow        32.0    30.0  15.0                                        590    Very slow    40.0    38.0  22.0                                        550    Very slow    Slow    Slow  Slow, 35% in 90                                                               minutes                                     500    Very slow    Very    Very  Slow, 5% in 100                                                 Slow    Slow  minutes                                     ______________________________________                                         *UF.sub.4 : -60 + 120 mesh                                               

The rates of reaction of UF₄ containing catalyst were substantiallyhigher than the rate of reaction of a sample of UF₄ which did notcontain any catalyst.

The effect of the particle size of the catalyst on the rate of reactionis illustrated by the following example. A catalyst consisting of 5 percent by weight of platinum on -300 mesh alumina was compressed intopellets under a pressure of 4 tons per square inch. These pellets werethen crushed and sieved into -35 + 85, -85 + 100, and -300 meshfractions. Samples of these three catalysts were then mixed with -60 +120 mesh UF₄ such that the final catalyst concentration in the UF₄ was 1per cent by weight. The rates of reaction were then measured at 640°C ona thermobalance and are shown in Table 2.

                  TABLE 2                                                         ______________________________________                                        EFFECT OF CATALYST MESH SIZE ON THE RATE OF                                   REACTION OF UF.sub.4 WITH OXYGEN*                                                               Time Required for 90%                                       Mesh Size of Catalyst                                                                           Reaction (mins)                                             ______________________________________                                        -300              10                                                          -85 + 100         16                                                          -35 + 85          20                                                          ______________________________________                                         *UF.sub.4 : -60 + 120 mesh, 640°C.                                

The results show that while a decrease in reaction rate is observed withan increase in the particle size of the catalyst, the rates at 640°C inthe presence of catalyst are very much higher than in the absence ofcatalyst (Table 1).

The effectiveness of several metals for the catalysis of the oxidationreaction (1) is illustrated in the following. A series of catalysts wereprepared, each consisting of 1 to 5 per cent by weight of the statedmetal supported on alumina. The rate of reaction of UF₄ containingconcentrations of 1 or 10 per cent by weight of catalyst with oxygen at640°C was measured on a thermobalance. The results are summarized inTable 3 and these indicate that in addition to platinum a number ofother metals in the platinum group, and also gold and silver, areeffective in promoting the rate of this reaction.

Cobalt oxide (Co₃ O₄) is also an effective catalyst for the oxidation ofUF₄ ; for example, the oxide in unsupported form when mixed at aconcentration of 10 per cent by weight with respect to UF₄ promotes therate of oxidation of UF₄ such that in the presence of the catalyst 50per cent of the UF₄ has reacted in 15 minutes, while in the absence ofcatalyst 50 per cent of the UF₄ reacted in 50 minutes -- see Table 3hereunder.

                  TABLE 3                                                         ______________________________________                                        SUMMARY OF THE ACTIVITY OF VARIOUS CATALYSTS                                  IN PROMOTING THE RATE OF THE REACTION OF                                      UF.sub.4 WITH OXYGEN AT 640°C                                                                 Catalyst     Time for                                                         Concentration                                                                              50%                                                              with respect to                                                                            Reaction                                  Catalyst  Type         UF.sub.4 (wt.%)                                                                            (min)                                     ______________________________________                                        Pt       5% on γ -Al.sub.2 O.sub.3                                                             1             7                                        Pt       2.5% on γ -Al.sub.2 O.sub.3                                                           1            10                                        Pt       1% on γ-Al.sub.2 O.sub.3                                                              1            12                                        Ru       5% on γ-Al.sub.2 O.sub.3                                                              1             9                                        Rh       5% on γ-Al.sub.2 O.sub.3                                                              1            20                                        Ir       5% on γ-Al.sub.2 O.sub.3                                                              1            20                                        Os       5% on γ-Al.sub.2 O.sub.3                                                              1            27                                        Pd       5% on γ-Al.sub.2 O.sub.3                                                              1            33                                        Au       5% on γ-Al.sub.2 O.sub.3                                                              10           28                                        Ag       5% on γ-Al.sub.2 O.sub.3                                                              10           45                                        Co.sub.3 O.sub.4                                                                       Unsupported   10           15                                        PtO.sub.2.x H.sub.2 O                                                                  Unsupported   1            14                                        Pt black Unsupported   1             9                                        Pt metal                                                                      filings  Unsupported   1            28                                        Uncatal-                                                                      ysed reac-                                                                    tion                   0            50                                        ______________________________________                                    

Hydrated platinum oxide (Adams Catalyst) and unsupported platinum,either in the form commonly known as platinum black, or in the form offinely divided platinum metal filings, are also effective in promotingthe rate of oxidation of UF₄ by oxygen (see Table 3).

Supports other than alumina are also effective in combination with theabovementioned metals in the catalytic oxidation of UF₄. Catalystsconsisting of 5 per cent by weight of platinum were prepared on bariumsulphate, magnesium oxide, silica and calcium fluoride by mixing thesecompounds separately with an aqueous solution containing an appropriateamount of cloroplatinic acid, evaporating the mixture to dryness andheating the solid so obtained in hydrogen gas at 400°C. It was observedthat the platinum supported on these materials, catalyzed the oxidationof UF₄ by oxygen, although these supports did not yield catalysts aseffective as those which used alumina as the support.

The same catalyst that is effective in catalyzing the oxidation of UF₄with oxygen is also effective in increasing the rate of reaction of UO₂F₂ with hydrogen. The following examples are described in order toillustrate the effect of the concentration of a catalyst and temperatureon the rate of reaction of UO₂ F₂ with hydrogen. A catalyst consistingof 5 per cent by weight of platinum on alumina was mixed with UO₂ F₂ atconcentrations of catalyst of 0.05, 0.1 and 1.0 per cent by weightrelative to UO₂ F₂, and heated at temperatures of 550°, 610° and 660°Cin a thermobalance. The resulsts (see Table 4 hereunder) show that therate of reaction of UO₂ F₂ with hydrogen in the presence of the catalystis considerably higher than in the absence of the catalyst.

                  TABLE 4                                                         ______________________________________                                        EFFECT OF TEMPERATURE                                                         AND CATALYST CONCENTRATION                                                    ON THE RATE OF REDUCTION OF UO.sub.2 F.sub.2 *                                ______________________________________                                                   Time Required for 90% Reaction (min)                               Temperature °C                                                                    Catalyst Concentration % by Weight                                          0       0.05      0.1       1.0                                      ______________________________________                                        550°C                                                                             60.0      52.0      34.0    25.0                                   610°C                                                                             31.0      19.0      15.0    12.0                                   660°C                                                                             17.0      10.5       7.0     5.0                                   ______________________________________                                         *UO.sub.2 F.sub.2 : -60 + 120 mesh?                                      

In addition to the platinum catalyst disclosed above, ruthenium,palladium, rhodium, iridium, gold, silver, copper oxide, cobalt oxide,platinium black, platinum oxide (Adams Catalyst), palladium oxide andnickel are also effective catalysts for the reduction of uranyl fluoride(see Table 5 hereunder).

                  TABLE 5                                                         ______________________________________                                        COMPARISON OF THE EFFECTIVENESS OF VARIOUS                                    CATALYSTS IN PROMOTING THE RATE                                               OF REDUCTION OF UO.sub.2 F.sub.2.sup.(B)                                      ______________________________________                                        Catalyst - Supported .sup.(A)                                                                     Time Required for 50%                                     5% w/w on Alumina   Reaction                                                                      UO.sub.3→→UO.sub.2 .sup.(C)                 ______________________________________                                        None                10.0                                                      Pt                  1.5                                                       Ru                  3.0                                                       Pd                  2.0                                                       Rh                  1.8                                                       Ir                  3.4                                                       Au                  8.5                                                       Ag                  5.0                                                       Pt black            1.0                                                       CuO                 10.0                                                      Catalyst - Unsupported .sup.(A)                                               CuO                 10.0                                                      Co.sub.3 O.sub.4    9.0                                                       Pt black            1.0                                                       PtO.sub.2.xH.sub.2 O                                                                              1.5                                                       PdO.sub.2           2.0                                                       Ni                  2.0                                                        .sup.(A) For all catalysed rates, the catalyst concentration is 1% w/w        with respect to UO.sub.2 F.sub.2 or UO.sub.3                                  .sup.(B) UO.sub.2 F.sub.2 : -60 + 120 BSS, 600°C                       .sup.(C) UO.sub.3 : denitrator derived, -120 + 150 BSS, 550°C     

The present invention discloses a catalyst which is effective incatalyzing the oxidation of UF₄ with oxygen, and the reaction of UO₂ F₂with hydrogen, and which may be recycled when the UO₂ product of thelatter reaction is converted to UF₄ for re-use. The following series ofexperiments illustrates that the catalyst is effective in catalysing theoxidation reaction even after several cycles through reactions (1), (2)and (3). A 2-g sample of UF₄ containing 1 per cent by weight of acatalyst consisting of 5 per cent by weight of platinum supported onalumina, was completely converted to UO₂ F₂ and UF₆ by heating in dryoxygen at 600°C for approximately 30 min. The UO₂ F₂ so formed was thenreduced to UO₂ by heating in an atmosphere of hydrogen gas at atemperature of approximately 500°C for approximately 30 min. The UO₂ wasthen converted to UF₄ by reaction with anhydrous HF at approximately500°C. As this UF₄ now contained approximately 2 per cent by weight ofcatalyst, it was mixed with an equal weight of UF₄ which did not containany catalyst. It was observed that this latter mixture of UF₄, now againcontaining 1 per cent by weight of catalyst, still reacted with oxygengas at 600°C at a rate which is comparable to that obtained from asample containing a catalyst which had not been subjected to the abovecycle. The above cycle was then repeated four times, the rate ofreaction of the UF₄ obtained after each recycle with oxygen gas wasmeasured at 640°C and, as shown in Table 6, no apparent loss of catalystactivity was observed after each cycle.

                  TABLE 6                                                         ______________________________________                                        EFFECT OF CATALYST RECYCLING ON THE                                           RATE OF REACTION OF UF.sub.4 WITH OXYGEN*                                     ______________________________________                                        Sample     Time Required for 50% Reaction (min)                               ______________________________________                                        Original   4.0                                                                1st recycle                                                                              3.5                                                                2nd recycle                                                                              3.5                                                                3rd recycle                                                                              3.6                                                                4th recycle                                                                              3.8                                                                UF.sub.4 without                                                              catalyst   50.0                                                               ______________________________________                                         *640°C, 1% w/w of catalyst, UF.sub.4 -60 + 120 BSS?               

The present invention also envisages that the UO₂ F₂ product containingthe catalyst may also be recycled by heating it in a mixture ofhydrogen-hydrogen fluoride at 400°-600°C, in place of the two separatestages described above.

The present invention discloses that the same catalyst that is effectivefor the oxidation of UF₄ with oxygen, and reduction of UO₂ F₂ withhydrogen, is also effective for increasing the rate of reduction of UO₃with hydrogen. The following example is described in order to illustratethis latter effect. A commercially-available catalyst consisting of 5per cent by weight of platinum on alumina powder was mixed with UO₃powder at a concentration of 1 per cent by weight relative to UO₃ andheated in hydrogen in a thermobalance at 550°C. The reaction wascomplete in 18 min in the presence of the catalyst compared with only 60per cent conversion to UO₂ in the same time in the absence of thecatalyst.

In addition to the platinum catalyst disclosed above, ruthenium,palladium, rhodium, iridium, gold, silver, copper oxide, cobalt oxide,platinum black, platinum oxide (Adams Catalyst), palladium oxide andnickel are also effective catalysts for the reduction of UO₃ by hydrogen(see Table 7 hereunder).

                  TABLE 7                                                         ______________________________________                                        COMPARISON OF THE EFFECTIVENESS                                               OF VARIOUS CATALYSTS IN PROMOTING                                             THE RATE OF REDUCTION OF UO.sub.3 .sup.(B)                                    ______________________________________                                        Catalyst - Supported                                                                          Time Required for 50% Reaction                                (A)             UO.sub.3 → UO.sub.2                                      5% w/w on                                                                   Alumina                                                                       ______________________________________                                        None            10.0                                                          Pt              1.5                                                           Ru              3.0                                                           Pd              2.0                                                           Rh              1.8                                                           Ir              3.4                                                           Au              8.5                                                           Ag              5.0                                                           Pt black        1.0                                                           CuO             10.0                                                          Catalyst - Unsuppor-                                                          ted .sup.(A)                                                                  CuO             10.0                                                          Co.sub.3 O.sub.4                                                                              9.0                                                           Pt black        1.0                                                           PtO.sub.2.xH.sub.2 O                                                                          1.5                                                           PdO.sub.2       2.0                                                           Ni              2.0                                                           ______________________________________                                         .sup.(A) For all catalysed rates, the catalyst concentration is 1% w/w        with respect to UO.sub.3                                                      .sup.(B) UO.sub.3 : denitrator derived, -120 + 150 BSS, 550°C     

By way of further examples of the production of UF₆ by the oxidation ofUF₄ in the presence of a catalyst the following experiments in tubefurnaces are described. A 6.67 g sample of UF₄ containing 1 per cent byweight of a catalyst containing 5 per cent by weight of platinum metalon alumina, was placed in a boat which in turn was placed in ahorizontal tube furnace, the furnace being heated to a temperature of610°C. Dry oxygen gas was passed through the furnace and over the UF₄and then through two consecutive nickel cold traps which contained aseries of baffle plates, the cold traps being maintained at atemperature of -80°C, at which temperature the UF₆ gas formed condensedto a solid of low vapor pressure. At the completion of the experimentthe residue in the boat was removed, weighed, and analyzed for uranium.The UF₆ condensed in the cold traps was transferred by sublimation to aweighed Teflon container. It was found that the weight of UO₂ F₂remaining in the boat was 3.05 g representing 93.2 per cent of thetheoretical yield, while the UF₆ collected weighed 1.81 g representing48.3 per cent of the theoretical yield. The results of similarexperiments summerized in Table 8 show that the yields of UO₂ F₂ were inthe range of 93 to 99 per cent of the theoretical, while the yields ofUF₆ were in the range 35 to 48 per cent of theoretical.

                                      TABLE 8                                     __________________________________________________________________________    YIELDS OF UF.sub.6 AND UO.sub.2 F.sub.2 FROM REACTION OF UF.sub.4 WITH        O.sub.2 IN THE PRESENCE OF                                                    1% OF W/W CATALYST AT 610°C                                            Weight of UF.sub.4                                                                     Weight of UO.sub.2 F.sub.2 at                                                            % Theoretical                                                                         Weight of UF.sub.6                                                                     % Theoretical yield of                   at start (g)                                                                           completion of                                                                            yield of                                                                              collected (g)                                                                          UF.sub.6                                          reaction (g)                                                                             UO.sub.2 F.sub.2                                          __________________________________________________________________________    6.67     3.05       93.2    1.81     48.3                                     4.20     2.03       99.0    1.01     42.5                                     4.00     1.85       94.3    0.78     34.8                                     __________________________________________________________________________

The low yields of UF₆ are due in part to the well-known difficultiesassociated with the quantitative condensation of small concentrations ofUF₆ and in part to the tendency of UF₆ to react with the nickel surfaceof the furnace tube according to the equation:

    UF.sub.6 + Ni → NiF.sub.2 + UF.sub.4                ( 4)

it is believed that the yield of UF₆ would be much improved if thereaction were carried out under large scale conditions where the ratioof nickel surface to UF₆ concentration is much smaller. Such conditionswould be encountered if the reaction were carried out either in afluidized or a moving bed reaction of a large diameter.

FIG. 1 is a flowsheet which illustrates the large scale production ofUF₆ in fluidized or moving bed reactors.

FIG. 2 is a flowsheet which additionally shows the recovery of HF.

FIG. 3 is a flowsheet which illustrate the production of UF₆ utilizingthe direct reduction of UO₃ to UO₂.

UF₄ and the catalyst are fed into the oxidation Reactor (A) where theUF₄ is converted by reaction (1) to UO₂ F₂ and UF₆. The gaseous effluentfrom the reactor is UF₆ and unconverted O₂. The UF₆ is separated from O₂in the cold trap (B). Unconverted O₂ can then be recycled back into theoxidation reactor. The solid effluent, UO₂ F₂ and catalyst and unreactedUF₄, is fed into the reduction reactor (C), where UO₂ F₂ is converted toUO₂ by reaction (2). The gaseous effluent from this reactor is HF andunreacted H₂. Both the product of the reduction reaction UO₂ and thecatalyst are the solid effluent from reactor (C) and this solid is thenfed to the hydrofluorination reactor (D). In this reactor UO₂ reactswith HF to form UF₄ according to equation (3). The gaseous effluent fromthe reactor is H₂ O + unreacted HF and the solid effluent is recycle UF₄and catalyst. HF can be seperated from the gaseous effluents of reactors(C) and (D) and used as feed for reactor (D). It should be noted thatthe starting material for the production of UF₆ can be either UO₂, UF₄,UO₂ F₂ or UO₃.

FIG. 2 differs from FIG. 1 in that it illustrates the recovery of HF inreactor (E). The gaseous effluent from reactors (C) and (D) are reactedwith UO₃ and the solid effluent from the reactor, UO₃ + UO₂ + UO₂ F₂ isfed to the reduction reactor (C). All unconverted UO₃ is reduced to UO₂in the reduction reactor according to equation 5 so that the feed to thehydrofluoroination reactor (D) is the same as for FIG. 1.

    uo.sub.3 + h.sub.2 → uo.sub.2 + h.sub.2 o           (5)

fig. 3 is the same as FIG. 2 only that UO₃ is fed to the reductionreactor (C) and is directly reduced to UO₂ according to equation 5.

Following from the disclosure of the present invention that theoxidation of UF₄ the reduction of UO₂ F₂ and the reduction of UO₃, canall be catalyzed by the same catalyst, FIGS. 2 and 3 illustratesimplified integrated processes using the same catalyst for theproduction of UF₆ from UO₃.

The present invention discloses that a fluidized bed may be usedsatisfactorily for the reaction of a mixture of particles of UF₄ andcatalyst with air or oxygen at a temperature of 500°-700°C for theproduction of UF₆ and UO₂ F₂. By way of example, a mixture of 160 g ofUO₂ F₂ and 40 g of UF₄ powder of -60 + 120 mesh containing 2 per cent byweight of a catalyst consisting of 5 per cent by weight of platinum onalumina of -60 + 120 mesh, was fluidized with a flow of 1.6 L/min ofoxygen gas in a 42 mm diameter fluidized bed reactor at 650°C for 30minutes, during which time the oxidation reaction was substantially (90per cent) complete. This rate of reaction is approximately the same as aconversion of 95 per cent obtained in experiments under similarconditions but without fluidization in a thermobalance. By comparison,in the absence of catalyst, only 35 per cent conversion was obtained in60 minutes under the same reaction conditions.

The above examples are merely illustrative and are not to be understoodas limiting the scope of our invention. It will be apparent to thoseskilled in the art that many variations in apparatus and procedure maybe employed without departing from the scope of our intention.

What we claim is:
 1. A method for the production of UF₆ comprisingreacting UF₄ with air or oxygen at a temperature of 500° to 700°C in thepresence of a catalyst selected from the group consisting of platinum,ruthenium, palladium, rhodium, osmium, iridium, gold, silver, nickel,copper oxide, cobalt oxide, platinum oxide and palladium oxide eitherunsupported or on a support selected from the group consisting ofalumina, magnesia, silica, calcium fluoride and barium sulphate.
 2. Amethod for the production of UF₆ comprising reacting UF₄ with air oroxygen at a temperature of 500° to 700°C in the presence of a catalystselected from the group consisting of platinum, ruthenium, palladium,rhodium, osmium, iridium, gold, silver, nickel, copper oxide, cobaltoxide, platinum oxide and palladium oxide either unsupported or on asupport selected from the group consisting of alumina, magnesia, silica,calcium fluoride and barium sulphate, reducing a by-product of thereaction (UO₂ F₂) in the presence of the same catalyst with hydrogen at400° to 600°C and reacting the reduction product (UO₂) with hydrogenfluoride in the presence of the same catalyst at 400° to 600°C toproduce UF₄ which is recycled for further reaction to produce UF₆.
 3. Amethod for the production of UO₂ comprising reacting UO₂ F₂ withhydrogen at a temperature of 400° to 600°C in the presence of a catalystselected from the group consisting of platinum, ruthenium, palladium,rhodium, iridium, gold, silver, nickel, copper oxide, cobalt oxide,platinum oxide and palladium oxide either unsupported or on a supportselected from the group consisting of alumina, magnesia, silica, calciumfluoride and barium sulphate.
 4. A method for the production of UF₄comprising reacting UO₂ with hydrogen fluoride at a temperature of 400°to 600°C in the presence of a catalyst selected from the groupconsisting of platinum, ruthenium, palladium, rhodium, iridium, gold,silver, nickel, copper oxide, cobalt oxide, platinum oxide and palladiumoxide either unsupported or on a support selected from the groupconsisting of alumina, magnesia, silica, calcium fluoride and bariumsulphate.
 5. A method for the production of UO₂ comprising reacting UO₃with hydrogen at a temperature of 400° to 600°C in the presence of acatalyst selected from the group consisting of platinum, ruthenium,palladium, rhodium, iridium, gold, silver, nickel, copper oxide, cobaltoxide, platinum oxide and palladium oxide either unsupported or on asupport selected from the group consisting of alumina, magnesia, silica,calcium fluoride and barium sulphate.
 6. A method for the production ofUF₆ comprising reacting UF₄ with air or oxygen at a temperature of 500°to 700°C in the presence of a catalyst selected from the groupconsisting of platinum, ruthenium, palladium, rhodium, osmium, iridium,gold, silver, nickel, copper oxide, cobalt oxide, platinum oxide andpalladium oxide either unsupported or on a support selected from thegroup consisting of alumina, magnesia, silica, calcium fluoride andbarium sulphate, reducing a by-product of the reaction (UO₂ F₂) andfresh UO₃ with hydrogen in the presence of the same catalyst at 400° to600°C, and hydrofluorinating the resulting mixture of solids in thepresence of the same catalyst at 400° to 600°C to produce UF₄ which isrecycled for further reaction to produce UF₆.
 7. A method as claimed inclaim 1 in which the UF₄ contains 0.1 to 5 percent by weight of saidcatalyst consisting of 0.1 to 5 percent by weight of platinum supportedon alumina.
 8. A method as claimed in claim 2 in which the UF₄ contains0.1 to 5 percent by weight of said catalyst consisting of 0.1 to 5percent by weight of platinum supported on alumina.
 9. A method asclaimed in claim 3 in which the UF₄ contains 0.1 to 5 percent by weightof said catalyst consisting of 0.1 to 5 percent by weight of platinumsupported on alumina.
 10. A method as claimed in claim 4 in which theUF₄ contains 0.1 to 5 percent by weight of said catalyst consisting of0.1 to 5 percent by weight of platinum supported on alumina.
 11. Amethod as claimed in claim 5 in which the UF₄ contains 0.1 to 5 percentby weight of said catalyst consisting of 0.1 to 5 percent by weight ofplatinum supported on alumina.
 12. A method as claimed in claim 6 inwhich the UF₄ contains 0.1 to 5 percent by weight of said catalystconsisting of 0.1 to 5 percent by weight of platinum supported onalumina.
 13. A method as claimed in claim 1 in which the UF₄ contains 1to 10 percent by weight of said catalyst which is a metal selected fromthe group consisting of ruthenium, osmium, palladium, iridium, rhodium,gold and silver at a concentration of 0.5 to 10 percent by weight onalumina.
 14. A method as claimed in claim 2 in which the UF₄ contains 1to 10 percent by weight of said catalyst, which is a metal selected fromthe group consisting of ruthenium, osmium, palladium, iridium, rhodium,gold and silver at a concentration of 0.5 to 10 percent by weight onalumina.
 15. A method as claimed in claim 6 in which the UF₄ contains 1to 10 percent by weight of said catalyst, which is is a metal selectedfrom the group consisting of ruthenium, osmium, palladium, iridium,rhodium, gold and silver at a concentration of 0.5 to 10 percent byweight on alumina.
 16. A method as claimed in claim 1 in which the UF₄contains 5 to 20 percent by weight of cobalt oxide (Co₃ O₄) as thecatalyst.
 17. A method as claimed in claim 2 in which the UF₄ contains 5to 20 percent by weight of cobalt oxide (Co₃ O₄) as the catalyst.
 18. Amethod as claimed in claim 6 in which the UF₄ contains 5 to 20 percentby weight of cobalt oxide (Co₃ O₄) as the catalyst.
 19. A method asclaimed in claim 1 in which the UF₄ contains 0.1 to 5 percent by weightof a catalyst added as hydrated platinum oxide.
 20. A method as claimedin claim 2 in which the UF₄ contains 0.1 to 5 percent by weight of acatalyst added as hydrated platinum oxide.
 21. A method as claimed inclaim 6 in which the UF₄ contains 0.1 to 5 percent by weight of acatalyst added as hydrated platinum oxide.
 22. A method as claimed inclaim 1 in which the UF₄ contains 0.1 to 5 percent by weight of platinumblack or platinum metal filings.
 23. A method as claimed in claim 2 inwhich the UF₄ contains 0.1 to 5 percent by weight of platinum black orplatinum metal filings.
 24. A method as claimed in claim 6 in which theUF₄ contains 0.1 to 5 percent by weight of platinum black or platinummetal filings.
 25. A method as claimed in claim 1 wherein the reactingof the UF₄ with the air or oxygen comprises adding the UF₄ and saidcatalyst to a fluidized bed of UO₂ F₂ particles which may also containcatalyst, removing the UF₆ in the gaseous phase and condensing the UF₆.26. A method as claimed in claim 2 wherein the reacting of the UF₄ withthe air or oxygen comprises adding the UF₄ and said catalyst to afluidized bed of UO₂ F₂ particles which may also contain catalyst,removing the UF₆ in the gaseous phase and condensing the UF₆.
 27. Amethod as claimed in claim 6 wherein the reacting of the UF₄ with theair or oxygen comprises adding the UF₄ and said catalyst to a fluidizedbed of UO₂ F₂ particles which may also contain catalyst, removing theUF₆ in the gaseous phase and condensing the UF₆.
 28. A method as claimedin claim 13 wherein the reacting of the UF₄ with the air or oxygencomprises adding the UF₄ and said catalyst to a fluidized bed of UO₂ F₂particles which may also contain catalyst, removing the UF₆ in thegaseous phase and condensing the UF₆.
 29. A method as claimed in claim14 wherein the reacting of the UF₄ with the air or oxygen comprisesadding the UF₄ and said catalyst to a fluidized bed of UO₂ F₂ particleswhich may also contain catalyst, removing the UF₆ in the gaseous phaseand condensing the UF₆.
 30. A method as claimed in claim 15 wherein thereacting of the UF₄ with the air or oxygen comprises adding the UF₄ andsaid catalyst to a fluidized bed of UO₂ F₂ particles which may alsocontain catalyst, removing the UF₆ in the gaseous phase and condensingthe UF₆.
 31. A method as claimed in claim 1 in which the UF₄ contains0.1 to 5 percent by weight of said catalyst, which consists of 0.1 to 5percent by weight of platinum supported on alumina, said reacting of theUF₄ with the air or oxygen comprising adding the UF₄ and catalyst to afluidized bed of UO₂ F₂ particles which may also contain catalyst,removing the UF₆ in gaseous state and condensing the UF₆.
 32. A methodas claimed in claim 2 in which the UF₄ contains 0.1 to 5 percent byweight of said catalyst, which consists of 0.1 to 5 percent by weight ofplatinum supported on alumina, said reacting of the UF₄ with the air oroxygen comprising adding the UF₄ and catalyst to a fluidized bed of UO₂F₂ particles which may also contain catalyst, removing the UF₆ ingaseous state and condensing the UF₆.
 33. A method as claimed in claim 6in which the UF₄ contains 0.1 to 5 percent by weight of said catalyst,which consists of 0.1 to 5 percent by weight of platinum supported onalumina, said reacting of the UF₄ with the air or oxygen comprisingadding the UF₄ and catalyst to a fluidized bed of UO₂ F₂ particles whichmay also contain catalyst, removing the UF₆ in gaseous state andcondensing the UF₆.